1. Field of the Invention
The present invention relates to a Cognitive Radio (CR)-based wireless communication system. More particularly, the present invention relates to an apparatus and method for enquiring available channel information in a CR-based wireless communication system.
2. Description of the Related Art
With advancements of wireless communication systems, the wireless communication systems are expected to provide various types of services. In addition, high-speed wireless data transmission techniques are required to provide various services with good quality in a reliable manner. Although various systems and schemes have been proposed for the high-speed wireless data transmission techniques, research on the high-speed data transmission techniques has continuously been conducted to transmit data in a faster and more cost effective manner. The wireless communication systems require additional frequency bands to support coexistence with conventional techniques. However, frequency resources are limited, and most of the frequency resources are currently occupied by existing systems.
Even if a frequency resource is occupied by a specific system, a corresponding frequency band is not always used. For this reason, recently, a method has been considered in which a time duration during which the frequency resource is not used is detected to use the frequency resource in the detected time duration. As such, a system devised to perform wireless communication by reusing the frequency resource occupied by the specific system and temporarily unused is referred to as a Cognitive Ratio (CR)-based wireless communication system. For example, a TeleVision (TV) band is defined as a band in which temporarily unused frequency resources are frequently generated. Accordingly, the Institute of Electrical and Electronics Engineers (IEEE) standard 802.22 has been established in order to solve problems and technical issues required to perform wireless communication by using the TV band without having an effect on a TV broadcast system.
The CR-based wireless communication system has to determine transmit power and an operational frequency band without generating interference with a licensed system. Therefore, the CR-based wireless communication system performs a process of recognizing a frequency band in use by the licensed system by utilizing a spectrum sensing function. Thereafter, the CR-based wireless communication system can only select an operational channel. In addition, if a signal of the licensed system is detected by continuous spectrum sensing while communication is performed through the selected operational channel, the CR-based wireless communication system no longer has to use the operational channel.
However, the spectrum sensing function does not guarantee correct recognition on whether a channel is used by the licensed system. In addition, signal detection and processing have to be carried out for a long period of time to perform the spectrum sensing which may result in performance deterioration in the CR-based wireless communication system.
Therefore, a need exists for a method for recognizing whether a channel is used by a licensed system in a CR-based wireless communication system.